1. Field of the Invention
The present invention relates to a technology for determining a piston position in each of the cylinders of an engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2004-044470 discloses an apparatus for detecting a piston position in each of the cylinders of an engine based on a combination of a reference crank angle position and a cam angle signal.
In the respective cylinders of a three-cylinder engine having respective pistons, the compression top dead centers appear in turn at an interval of crank angle of 240 degrees during the rotation of the crank shaft, and the compression top dead centers of three respective cylinders occur at every position of the crank angle spaced apart by 120 degrees.
Accordingly, in the case where the piston position determination is performed in the three-cylinder engine, it is necessary to determine whether or not it is the determination timing for each stroke phase difference, at each time when the crank angle position reaches the reference crank angle position at each crank angle of 120 degrees, and further, when determination is made that it is the determination timing for each stroke phase difference, it is necessary to determine which one of the cylinders is on a predetermined piston position.
Further, in an engine provided with a variable valve timing mechanism which varies the phase of a camshaft relative to a crankshaft, valve timing may be detected based on a phase difference between a cam angle signal output from a detection device disposed on the camshaft and a crank angle signal output from a detection device disposed on the crankshaft.
Therefore, in a conventional technology, in the case where determination of the piston position in each cylinder of the three-cylinder engine is executed accompanying execution of detecting of the valve timing, such a function might be requested to exhibit that the cam angle signal is generated at a minute interval.
However, in the case where the cam angle signal is generated by, for example, using a sensor in which an electromagnetic pickup detects protruding portions disposed on a signal plate, since the resolution of the above-mentioned sensor is low, it is difficult to realize the above-described function and also to ensure the stable detection precision.